Earth Science, 11e

Earth’s History: A Brief Summary

Chapter 12

Precambrian era

4.5 billion to 540 million years ago88% of Earth's history Only sketchy knowledge Most Precambrian rocks are devoid of

fossils

Precambrian era

Precambrian rocks • Most are buried from view • Each continent has a "core area" of

Precambrian rocks called a shield • Extensive iron ore deposits • Absent are fossil fuels

Continental structures today

Figure 12.3

Precambrian era

Earth's atmosphere• Primitive atmosphere formed from volcanic

gases • A process called outgassing • Water vapor, carbon dioxide, nitrogen, and several

trace gases • Very little free oxygen

• Water vapor condenses and forms primitive oceans as Earth cools

Precambrian era

Earth's atmosphere• Bacteria evolve • Plants evolve and photosynthesis produces

oxygen • Oxygen content in the atmosphere increases • By about 4 billion years after Earth formed,

abundant ocean-dwelling organisms that require oxygen existed

Precambrian era

Precambrian fossils• Most common are stromatolites

• Material deposited by cyanobacteria (formerly called “blue green algae”)

• Common about 2 billion years ago • Microfossils of bacteria and algae have been

found in chert • Southern Africa (3.1 billion years of age)• Lake Superior area (1.7 billion years of age)

Modern Day StromatolitesStromatolites are rocky structures made by photosynthetic cyanobacteriawhich secrete a glue that binds sediment particles. Ancient stromatolites dominated coastal areas 3.5 to 1.2 billion years ago. The oxygen they produced transformed Earth’s atmosphere to oxygen-rich. Now they exist in only a few locations. The ones pictured here are near Shark Bay, Australia.

Precambrian era

Precambrian fossils• All life was in the ocean during the Precambrian• Plant fossils date from the middle Precambrian • Animal fossils date from the late Precambrian• Animals were all invertebrates (no backbone)

with no hard parts• Diverse and multicelled organisms exist by the

close of the Precambrian• Fossil record of Precambrian is very meager

The geologic time scale

Figure 12.2

Paleozoic era

540 million years ago to about 248 million years ago First life forms with hard parts, possibly due

to oxygen enrichment in the oceansAbundant Paleozoic fossils Early Paleozoic history

• Southern continent of Gondwanaland exists

Paleozoic era

Early Paleozoic history • North America

• A barren lowland • Seas move inland and recede several times and

shallow marine basins evaporate leaving rock salt and gypsum deposits

• Taconic orogeny, a mountain building event, affects eastern North America

Reconstruction of Earth in early Paleozoic time

Figure 12.7

The Cambrian Explosion

• Beginning of Cambrian Period, 540 million years ago

• Most major animal groups started to appear in the fossil record within a geologically short time

• Rapid expansion of different forms of life on Earth

• Evolution of hard parts as defense against predators

• Predators eventually developed hard parts

• Hard parts allowed better preservation and more diverse fossil record

Paleozoic era

Early Paleozoic life • Restricted to seas• Vertebrates had not yet evolved • Life consisted of several invertebrate groups

• Trilobites• Brachiopods• Cephalopods

• First organisms with hard parts, such as shells –perhaps for protection

Natural cast of a trilobite

Figure 12.5 A

Trilobites: Diversity of shapes and sizes

Most trilobites were small (1 or 2 inches), but some were giants, such as Isotelus, which measured 27 inches long.

Brachiopods: Fossil and ModernBrachiopods are much less common today than during the Paleozoic Era. Although they look like clams, mussels, oysters, and scallops (bivalves), brachiopods are not related to bivalves. Lingula is a modern brachiopod.

Cambrian Super PredatorAnomalocaris was a giant shrimp up to 6.5” feet long, with

compound eyes (18,000 lenses each), grasping arms, and jaws.

Anomalocaris: Terror of the Cambrian PeriodBigger, faster, and with better vision than any creature in the Cambrian seas, Anomalocaris preyed on trilobites, or anything it could catch and kill. A mass extinction marked the end of the Cambrian Period, and Anomalocaris also went extinct.

Anomalocaris pursues a trilobite

Cephalopods dominate the Ordovician PeriodEarly cephalopods included this nautiloid called Cameroceras, which

grew to about 25 feet long, and fed on shellfish and other cephalopods.

Nautiloids: Giants of the Ordovician

Eurypterids: Giant Sea Scorpions (Silurian Period)

Life sized model of a giant eurypterid

Devonian Period: The Age of FishesArmored fishes, sharks, and bony fish evolved. A top predator was the monstrous 26 foot long armored Dunkleosteus.

Dunkleosteus

Armored fish became extinct by the end of the Devonian Period.

Placoderm: Devonian armored fish

Paleozoic era

Late Paleozoic life • Organisms diversified dramatically • Land plants • Fishes evolve into two groups of bony fish

• Lung fish• Lobe-finned fish which become the amphibians

• Insects invade the land• Amphibians diversify rapidly • Extensive coal swamps develop

Late Devonian to Early Pennsylvanian Periods

Late Devonian: Lungfish evolve to Amphibians

Early Pennsylvanian Period

Carboniferous Period (Mississippian-Pennsylvanian)

Pennsylvanian Period coal swamp composed of giant seed ferns that later became the great coal deposits of the future.

Permian Period: Rise of the ReptilesPelycosaurs such as the sail back carnivore Dimetrodon were not dinosaurs, but therapsids (“mammal-like” reptiles). Evolving at the same time during the Late Permian Period were the archosaurs, ancestors of the dinosaurs.

Evolution of major groups of organisms

Figure 12.6

Paleozoic era

Late Paleozoic history • Supercontinent of Pangaea forms • Several mountain belts formed during the

movements of the continents • World's climate becomes very seasonal, causing

the dramatic extinction of many species

Formation of Pangaea in late Paleozoic time

Figure 12.10 C

The Great End-of-Permian Mass Extinction• 252 million years ago, at the end of the Permian Period, marking the

end of the Paleozoic Era

• Massive volcanic eruptions of the Siberian Traps (Siberia, Russia) spewed out over 4 million cubic kilometers of lava

• Caused the sudden global wipeout of 96% of aquatic and 70% of land species, including entire groups that had survived for hundreds of millions of years (trilobites)

• Volcanic eruptions released huge amounts of sulfur dioxide and carbon dioxide into the air, heating up the atmosphere and acidifying the oceans

• The mass extinction paved the way for the age of reptiles, where dinosaurs ruled the land, marine reptiles ruled the seas, and flying reptiles ruled the air during the Mesozoic Era.

Mesozoic era

248 million years ago to about 65 million years ago Often called the “age of dinosaurs”Mesozoic history

• Begins with much of the world's land above sea level

• Seas invade western North America • Breakup of Pangaea begins forming the

Atlantic Ocean

Mesozoic era

Mesozoic history • North American plate began to override the

Pacific plate • Mountains of western North America began

forming Mesozoic life

• Survivors of the great Paleozoic extinction • Gymnosperms become the dominant trees

Mesozoic era

Mesozoic life • Reptiles (first true terrestrial animals) readily

adapt to the dry Mesozoic climate • Reptiles have shell-covered eggs that can be

laid on the land • Dinosaurs dominate • One group of reptiles led to the birds • Many reptile groups, along with many other

animal groups, become extinct at the close of the Mesozoic

Marine reptiles evolved separately from dinosaurs during Triassic

Dinosaurs: Built for Success

• Dinosaurs walked with an erect gait, with the legs straight under the body

• Crocodiles and lizards walk with a sprawling gait, with the legs held outwards and elbows bent.

Reconstruction of Earth in the late Jurassic period

Figure 12.13 B

Sauropods: the largest of all dinosaurs• Some exceeded 100 feet in length, and 60 tons in weight• Their main food were the leaves of conifer trees

Apatosaurus: formerly known as Brontosaurus

Brachiosaurus: a titanosaur (long forelimbs)

Stegosaurus: Walking tank of the Jurassic

Allosaurus: Top predator of the Jurassic

Allosaurus

Allosaurus chasing a fleet-footed Dryosaurus

SpinosaurusLarger (50 feet long, 9 tons) than Tyrannosaurus Rex, but the two predators never met, living 20 millions of years apart and on different continents.

Pteranodon

Pteranodon

Hadrosaurs

ParasaurolophusThe spectacular head crest was a hollow tube that could generate the low-pitched sound of a fog horn, useful for mating calls and for warning other herd members without being located by a predator.

Daspletosaurus and Lambeosaurus

Stegosaurs (Jurassic), Ankylosaurs and Nodosaurs (Cretaceous)

Ankylosaurs and Nodosaurs (Cretaceous)

Ankylosaurus: Cretaceous walking tank

• Covered head to toe with bony armor plates and spikes• tail club could break the ankles of a Tyrannosaurus

Ceratopsians: Last dinosaur group to evolve

Protoceratops and Velociraptor fight

From the fossils found, both dinosaurs were in a fight to the death, and both died abruptly after being buried in a sandstorm

Velociraptor fossil

Recent fossil evidence showed that Velociraptor had feathers

Despite depictions in the Jurassic Park movies, Velociraptor was only the size of a turkey.

The Utahraptor is much larger than Velociraptor and closer to what was depicted in the Jurassic Park movies. Despite recent evidence of raptors being feathered, the movies left the feathers off because feathered dinosaurs were deemed less menacing.

Large raptor species

CeratopsiansCharacterized by horns, frills made of bone (sometimes with spikes), huge heads, a ball-and-socket neck joint, powerful jaws for chewing tough plants on the ground

The last species to evolve was the largest, Triceratops

Recently discovered Ceratopsians

Tyrannosaurus Rex vs. Triceratops

Alamosaurus: Last of the sauropodsTitanosaurs such as Alamosaurus actually had thin body armor

Even Tyrannosaurus Rex may have had feathers

Tyrannosaurus Rex, reconstructed in its modern pose

Sue, the T. Rex had a skull 4 feet long, with serrated teeth up to 8” long, with the most powerful bite force of any creature ever

Quetzalcoatlus had a 33-foot wing span

Quetzalcoatlus, the largest known pterosaur,with a 33-foot wing span, reconstructed to full size. It could spot a dinosaur eggs nest from the sky, and swoop down to eat baby T. rex hatchings in one gulp.

Cold-blooded vs. Warm-bloodedCold Blooded (Ectothermic)

Dinosaurs, Reptiles, AmphibiansWarm Blooded (Endothermic)

Mammals, BirdsBody temperature fluctuates with the surrounding environment

Body temperature is constant, despite fluctuations in the environment

Basking in the sun is often needed to allow activity, sluggish in cold weather

Allows constant activity and can live in all climates

Can eat less often (a large meal can last for weeks)

Has to eat more often to maintain body temperature

Low temperatures can induce hibernation and eventually death

High temperatures cause brain damage and death

Most dinosaurs were large enough prevent loss of body heat

Ice age mammals tended to be large to and furry to mitigate heat loss

Dinosaurs enjoyed a warmer climate and no continental glaciation at all

The Cenozoic Era had many episodes of continental glaciation

Most dinosaurs were cold blooded and laid eggs.

Birds are warm-blooded. Perhaps small dinosaurs (raptors) were too.

The Extinction of the DinosaursAfter ruling the earth for over 150 million years (more than twice as long as mammals), the dinosaurs, marine reptiles, and flying reptiles were all wiped out in a sudden mass extinction, caused by an asteroid impact at the end of the Cretaceous Period that set off a worldwide chain of catastrophes.

Alvarez Asteroid Impact Theory (1980)Luis Alvarez (physicist) and his son, Walter Alvarez (geologist) stand by a rock outcrop pointing out the K-T (Cretaceous-Tertiary) boundary clay layer that contains enriched amounts of the rare element iridium. Their research showed that a 6-mile wide asteroid struck Earth 65 million years ago.

Alvarez Asteroid Impact Theory (1980)

• During the late 1970s, Walter Alvarez and his team investigated what caused the worldwide enrichment of iridium in a layer of clay that marked the K-T boundary

• Dinosaur fossils were found only below the clay layer (Cretaceous Period) and none were found above it (Tertiary)

• Iridium is rare in rocks on earth, but is common in meteorites and asteroids

• Evidence supporting the impact theory:• Iridium enrichment found worldwide at the K-T boundary• Shocked quartz (stishovite) grains that could only be made by meteorite

impact• Micro-tektites (small volcanic glassy objects made by meteorite impact)• Soot deposits (carbon deposits) as evidence of huge forest fires• Overturned sediments and meteorite buried miles deep in a crater in

Chicxulub, Mexico

Alvarez Asteroid Impact Theory (1980)• Luis Alvarez made calculations for an asteroid/meteorite impact

that could have distributed the iridium, and came up with a 6-mile wide rock that struck Earth at 40,000 mph

• The impact packed the energy of over 1 billion Hiroshima atomic bombs, which caused wave upon wave of catastrophic events

• The search for the impact site considered a number of sites, but the best candidate was found in the Yucatan Peninsula in the Gulf of Mexico, a place called Chicxulub

• The asteroid struck the Gulf of Mexico at a low angle of about 30 degrees aimed northwest.

• Unfortunately, the rocks beneath the Gulf of Mexico contained gypsum; the impact released huge amounts of sulfur dioxidethat caused prolonged sunlight blockage and severe acid rain that destroyed the land and ocean ecosystems.

• Debated for 30 years, it was accepted by scientific consensus

Alvarez Asteroid Impact Theory (1979)

The asteroid disintegrated upon impact in the Gulf of Mexico. causing a cascading wave of catastrophes:

• Rain of falling molten rock and boulders near the impact site• Hurricane force winds near the impact site• Ejecta cloud in upper atmosphere that baked the surface to 300 F.• Huge dust storms• Massive forest fires and fire storms• Earthquakes at Magnitude 11• Mega-tsunamis that struck all coastal areas• Prolonged blockage of sunlight by the dust and debris• Severe acid rain that lowered the pH of the oceans• Die off of algae and land plants• Lowered global temperatures• Starvation of plant eating dinosaurs and eventually the carnivores

Mesozoic era

Mesozoic life• Many reptile groups, along with many other

animal groups, become extinct at the close of the Mesozoic

• One theory is that a large asteroid or comet struck Earth (widely accepted by scientific consensus after 30 years of debate in 2010)

• Another possibility is extensive volcanism (Deccan Traps)

What groups survived the great Cretaceous mass extinction?

• Mammals, birds, smaller reptiles and amphibians survived because they were small and could seek shelter underground, but dinosaurs and flying reptiles were too big to do so

• Marine reptiles had to stay near the ocean surface to breathe air, and perished; other fish stayed in deep water to survive

• Mammals had evolved alongside the dinosaurs, surviving by staying out of their way, inheriting the earth only when the dinosaurs were wiped out

• Land plants eventually recovered, with ferns being the first to colonize the ravaged earth

• Mammals diversified and some became large• The Cenozoic is called the age of mammals• Humans owe their existence to the extinction of the dinosaurs

Major reptile groups in the Mesozoic era

Figure 12.16

What if the dinosaurs had survived the asteroid impact? They might still rule the earth today instead of mammals, and might look like this:

Cenozoic era

65 million years ago to the presentOften called the “age of mammals”Smaller fraction of geologic time than either

the Paleozoic or the Mesozoic North America

• Most of the continent was above sea level throughout the Cenozoic era

Cenozoic era

North America • Many events of mountain building, volcanism,

and earthquakes in the West • Eastern North America

• Stable with abundant marine sedimentation • Eroded Appalachians were raised by isostatic

adjustments

Cenozoic era

North America • Western North America

• Building of the Rocky Mountains was coming to an end

• Large region is uplifted • Basin and Range Province formed • Re-elevates the Rockies • Rivers erode and form gorges (e.g., Grand

Canyon and Black Canyon)

Cenozoic era

North America • Western North America

• Volcanic activity is common • Fissure eruptions form the Columbia Plateau • Volcanoes form from northern California to the

Canadian border • Coast Ranges form • Sierra Nevada become fault block mountains

Cenozoic era

Cenozoic life • Mammals replace reptiles as the dominant land

animals • Angiosperms (flowering plants with covered

seeds) dominate the plant world • Strongly influenced the evolution of both birds and

mammals • Food source for both birds and mammals

Cenozoic era

Cenozoic life • Two groups of mammals evolve after the

reptilian extinctions at the close of the Mesozoic

• Marsupials • Placentals

Wooly Mammoths & Mastodons (extinct, Pleistocene)

American Lion (extinct)lived in North America during Pleistocene Epoch

Smilodon(extinct North American saber-tooth cat)

Giant Short Faced Bear(Extinct North American top predator during Pleistocene)

Cenozoic era

Cenozoic life • Mammals diversify quite rapidly and some

groups become very large • e.g., Hornless rhinoceros, which stood nearly 16 feet

high • Many large animals became extinct

• Humans evolve

End of Chapter 12